Method and apparatus for correcting I/Q mismatch in a wireless communication signal

ABSTRACT

Briefly, some embodiments of the invention may provide devices, systems and methods of in-phase and quadrature mismatch analysis and correction. For example, a method in accordance with an embodiment of the invention may include re-encoding an estimated symbol of an input signal having an in-phase component and a quadrature component, based on an analysis of a mismatch between said in-phase component and said quadrature component.

CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure is a continuation of and claims priority to U.S.patent application Ser. No. 13/425,179, filed Mar. 20, 2012, now U.S.Pat. No. 8,428,180, issued Apr. 23, 2013, which is a continuation of andclaims priority to U.S. patent application Ser. No. 10/949,330, filedSep. 27, 2004, now U.S. Pat. No. 8,144,806, issued Mar. 27, 2012, whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

A first wireless communication device may transmit data using anIn-phase (I) signal and a Quadrature (Q) signal, which may have aphase-shift of 90 degrees relative to the I signal. The I and Q (I/Q)signals may be received by a second wireless communication device, andmay have an I/Q mismatch. For example, an I/Q mismatch may occur whenthe gain of the I signal is different from the gain of the Q signal, orwhen the phase-shift between the I and the Q signals in not exactly 90degrees. An I/Q mismatch, for example, may impair the ability of thesecond wireless communication device to correctly receive and processdata carried by the I/Q signals, or may impair performance of the secondcommunication device, e.g., in high Signal to Noise Ratio (SNR)communications.

Some wireless communication devices may partially mitigate problemsrelated to I/Q mismatch by utilizing highly precise components havingmatching amplitude and phase characteristic. However, such highlyprecise components may be very expensive, and their utilization maystill result in some I/Q mismatch errors.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with features and advantages thereof, may best be understood byreference to the following detailed description when read with theaccompanied drawings in which:

FIG. 1 is a schematic block diagram illustration of a wirelesscommunication system including one or more wireless communicationdevices utilizing I/Q mismatch correction in accordance with exemplaryembodiments of the invention;

FIG. 2 is a schematic block diagram illustration of a wirelesscommunication device utilizing I/Q mismatch correction in accordancewith exemplary embodiments of the invention; and

FIG. 3 is a schematic flow-chart of a method of I/Q mismatch correctionin accordance with exemplary embodiments of the invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those of ordinary skill in the artthat the invention may be practiced without these specific details. Inother instances, well-known methods, procedures, components, unitsand/or circuits have not been described in detail so as not to obscurethe invention.

It should be understood that embodiments of the invention may be used ina variety of applications. Although the invention is not limited in thisrespect, embodiments of the invention may be used in conjunction withmany apparatuses, for example, a receiver, a transceiver, atransmitter-receiver, a wireless communication station, a wirelesscommunication device, a wireless Access Point (AP), a processor, acontroller, a modem, a wireless modem, a Personal Digital Assistant(PDA) device, a cellular telephone, a wireless telephone, a PersonalCommunication Systems (PCS) device, a PDA device which incorporates awireless communication device, or the like.

FIG. 1 schematically illustrates a block diagram of a wirelesscommunication system 100 including one or more wireless communicationdevices utilizing I/Q mismatch correction in accordance with exemplaryembodiments of the invention. System 100 may include one or morewireless communication devices, for example, devices 101 and 102.

Device 101 and device 102 may communicate between themselves over ashared wireless media 120, which may include, for example, wirelesscommunication links 111 and 112. For example, device 101 may communicatewith one or more other devices of system 100 through link 111, anddevice 102 may communicate with one or more other devices of system 100through link 112.

In accordance with some embodiments of the invention, device 101 maytransmit a wireless communication signal having In-phase (I) andQuadrature (Q) components (referred to herein as “I/Q signal”). Asdescribed in detail below, device 102 may receive the I/Q signal,estimate a channel and symbols, re-encode the symbols, and calculate andcorrect an I/Q mismatch. Device 102 may repeat these operations as maybe necessary to sufficiently reduce or eliminate the I/Q mismatch.

FIG. 2 schematically illustrates a block diagram of a wirelesscommunication device 200 utilizing I/Q mismatch correction in accordancewith exemplary embodiments of the invention. Device 200 may be anexample of device 101 and/or device 102. Device 200 may include, forexample, a transmitter 201, a receiver 202, an antenna 203, a memoryunit 204, an input unit 205, an output unit 206, a power source 207, adown-converter 230, and a processor 210. Device 200 may include othersuitable hardware components and/or software components.

Transmitter 201 may include, for example, a Radio Frequency (RF)transmitter able to transmit wireless communication signals. Receiver202 may include, for example, a RF receiver able to receive wirelesscommunication signals. In some embodiments, transmitter 201 and receiver202 may be implemented in the form of a transceiver, atransmitter-receiver, or one or more units able to perform separate orintegrated functions of transmitting and/or receiving wirelesscommunication signals, blocks, frames, packets, messages and/or data.

Antenna 203 may include an internal and/or external RF antenna. In someembodiments, for example, antenna 203 may include a dipole antenna, amonopole antenna, an omni-directional antenna, an end fed antenna, acircularly polarized antenna, a micro-strip antenna, a diversityantenna, or any other type of antenna suitable for sending and/orreceiving wireless communication signals, blocks, frames, packets,messages and/or data.

Memory unit 204 may include, for example, a Random Access Memory (RAM),a Read Only Memory (ROM), a Dynamic RAM (DRAM), a Synchronous DRAM(SD-RAM), a Flash memory, a volatile memory, a non-volatile memory, acache memory, a buffer, a short term memory unit, a long term memoryunit, or other suitable memory units or storage units. In someembodiments, for example, memory unit 204 may store data transmitted orreceived by device 200.

Input unit 205 may include, for example, a keypad, a keyboard, one ormore keys, a touchpad, a joystick, a mouse, a pointing device, a userinterface, one or more buttons, one or more switches, one or moresliders, an on/off button or switch, or other suitable input components.In some embodiments, input unit 205 may input a suitable audio inputcomponent, e.g., an internal or external microphone, and/or a suitablevideo input component, e.g., an internal or external photo camera or avideo camera.

Output unit 206 may include, for example, a screen or monitor. In someembodiments, output unit 206 may include a suitable audio outputcomponent, e.g., one or more speakers, earphones or headphones. Outputunit 206 may optionally include other types of indicators, for example,a vibrator able to vibrate, or a Light Emitting Diode (LED) able toilluminate.

Power source 207 may include one or more batteries or power cells, whichmay be external and/or internal, rechargeable or non rechargeable. Powersource 270 may provide power to one or more components of device 200.

Down-converter 230 may include, for example, a circuit or unit able todown-convert a received signal having I and Q components (referred toherein as “I/Q signal”). For example, in one embodiment, down-converter230 may include two processing paths as is known in the art, e.g., usingmixers, a Local Oscillator (LO), a 90 degrees phase-shifter, Band PassFilter (BPF) units, Analog to Digital (A/D) converters, and Low PassFilter (LPF) units.

Processor 210 may include, for example, a Central Processing Unit (CPU),a Digital Signal Processor (DSP), a baseband processor, anapplication-side processor, a processor core, a microprocessor, acontroller, a circuit, circuitry, an Integrated Circuit (IC), aplurality of controllers and/or circuits, a chip, a microchip, or anyother suitable multi-purpose or specific processor, circuit orcontroller. In some embodiments, for example, processor 210 may performprocessing operations which may be used in producing signals transmittedby device 200 or in processing signals received by device 200. Processor210 may include one or more sub-units, for example, an Automatic GainControl (AGC) unit 211, an I/Q mismatch analysis and correction unit212, a channel estimator 213, an equalizer 214, and an encoder orre-encoder 215. It is noted that in some embodiments, one or more ofthese sub-units may be implemented as separate units which may beexternal or internal to processor 210, or as one or more softwaremodules, software components, micro-code and/or hardware components.

In accordance with some embodiments of the invention, receiver 202 mayreceive an input signal, e.g., an incoming wireless signal, which mayinclude an I component and a Q component. Down-converter 230 maydown-convert the I/Q signal as is known in the art. The I/Q signal maybe transferred to processor 210, e.g., to AGC 211 of processor 210,which may control the gain of the I/Q signal as is known in the art.

In some embodiments, channel estimator 213 may estimate a channel basedon a Training Sequence (TS) included in the I/Q signal. Then, symbolstransmitted in the I/Q signal may be estimated, for example, usingequalizer 214 or another suitable sub-optimal decision mechanism, e.g.,a mechanism based on a strongest survivor scheme.

In accordance with some embodiments of the invention, the estimatedsymbols may be re-encoded, for example, using encoder or re-encoder 215.The re-encoded symbols may be transferred to the I/Q analysis andcorrection unit 212, which may perform I/Q analysis operations and/orI/Q correction operations based on a pre-defined scheme or algorithm;for example, in some embodiments, correction unit 212 may estimate anI/Q mismatch using one or more Least Mean Square (LMS) calculations,e.g., using an LMS algorithm similar to the algorithm presented inpseudo-code as Code 1 and described in detail below. The estimated I/Qmismatch may be corrected or cancelled, for example, by correction unit212, based on applying a pre-defined correction matrix or correctionfunction, e.g., using a correction function as reflected in Code 1below. After the appropriate correction operations are applied, thechannel may be re-estimated using channel estimator 213 based on thecorrected signal, and the symbols may be re-estimated using equalizer214.

In some embodiments of the invention, the process of re-encoding thesymbols using re-encoder 215, performing I/Q mismatch analysisoperations and correction operations using correction unit 212,estimating the channel using cannel estimator 213, and estimating thesymbols 214, may be performed once or may be repeated a number of times.In one embodiment, for example, a pre-determined number of iterations,e.g., two iterations, of the above-described operations may beperformed. In some embodiments, for example, the number of iterationsmay be based on one or more pre-defined criteria, e.g., iterations maybe repeated until a calculated I/Q mismatch is smaller than apre-defined threshold value, or until a predefined period of timeelapses.

In one embodiment, optionally, in a first iteration, the estimationoperations performed by channel estimator 213 on the TS, may beperformed on a TS that already passed through correction unit 212, e.g.,for an initial I/Q mismatch correction and/or analysis. In anotherembodiment, in a first iteration, a non-corrected TS may be used forinitial channel estimation, e.g., as the TS may be too short to allow areliable I/Q mismatch or analysis process.

In one embodiment, the I/Q mismatch analysis and correction unit 212 mayinclude an analysis module and a correction module, implemented usinghardware components and/or software components, integrated as one unit.In another embodiment, the I/Q mismatch analysis and correction unit 212may include a plurality of sub-modules or sub-components, for example,an analyzer module or analyzer unit to perform an analysis of the I/Qmismatch, and a correction unit to perform correction operations or tocorrect an I/Q mismatch.

It is noted that in some embodiments, the handling of the I/Q mismatchmay allow, for example, reduction or elimination of the I/Q mismatch,and may be followed by other processing operations to further processthe I/Q signal as is known in the art.

In some embodiments, correction unit 212 may utilize a pre-definedalgorithm, code, function, correction matrix, or other suitable scheme,to perform I/Q mismatch analysis operations and correction operations.In one embodiment, for example, correction unit 212 may use an algorithmbased on the following pseudo-code:

-   for index 1=1:Niterations:-   %Correction Matrix:-   Cor=1/(sqrt(B_est)*cos(T_est))*B_est*cos(T_est/2)−sin(T_est/2) . . .    -   B_est*sin(T_est/2)cos(T_est/2)];-   %d(cor)/d(T_est):-   B1=sin(T_est)/(sqrt(B_est)*(cos(T_est))^2)*[B_est*cos(T_est/2)−sin(T_est/2)    . . .    -   ; −B_est*sin(T_est/2)cos(T_est/2)] . . .    -   −1/(sqrt(B_est)*cos(T_est))*[B_est/2*sin(T_est/2)½*cos(T_est/2)        . . .    -   ; B_est/2*cos(T_est/2)½*sin(T_est/2)];-   %d(cor)/d(B_est):-   B2=−1/(2*B_estl^1.5*cos(T_est))*[B_est*cost(T−est/2)−sin(T_estl2) .    . .    -   ; −B_est*sin(T_est/2)cos(T_est/2)] . . .    -   +1/(sqrt(B_est)*cos(T_est))*[cos(T_est/2) 0 . . .    -   ; −sin(T_est/2) 0];-   B1_vector=B1(1,1)+B1(1,2)+j*(B1(2,1)+B1(2,2));-   B2_vector=B2(1,1)+B2(1,2)+j*(B2(2,1)+B2(2,2));-   %Pass Received Samples via Correction Matrix:-   for index2=1:Nsamples    -   x=Cor*[real(Vf(index)); imag(Vf(index2))];    -   Vfcor(index2)=x(1)+j*x(2);    -   B1xlQvec(index2)=B1_vector;    -   B2xlQvec(index2)=B2_vector;-   end;-   SqrErr=(Vfcor−K*Vm);-   dSqrErr_dB_est=2*real(SqrErr).*real(B2xlQvec)+2*imag(SqrErr).*imag(B2xlQvec);-   dSqrErr_dT_est=2*real(SqrErr).*real(B1xlQvec)+2*imag(SqrErr).*imag(B1xlQvec);-   B_est=B_est+sign*StepSize_B*sum(dSqrErr_dB_est);-   T_est=T_est+sign*StepSize_T*sum(dSqrErr_dT_est);-   end;    -   Code 1        wherein:    -   Cor may indicate an I/Q mismatch correction matrix;    -   B_est may indicate a gain mismatch estimation;    -   T_est may indicate a phase mismatch estimation;    -   Vcor may indicate a signal after I/Q mismatch correction;    -   Vm may indicate an expected signal, e.g., re-encoded symbols;    -   Vf may indicate a received signal, e.g., having an I/Q mismatch;    -   B1 may indicate d(cor)/d(T_est);    -   B2 may indicate d(cor)/d(B_est);    -   SqrErr, may indicate a complex error function between Vm and Vf;    -   dSqrErr_dB_est may indicate the gradient of SqrErr with respect        to B_est; and    -   dSqrErr_dT_est may indicate the gradient of SqrErr with respect        to T_est.

Although embodiments of the invention are not limited in this regard,execution of Code I may apply a correction matrix, Cor, which may be theinverse matrix of a gain and/or phase mismatch model corresponding tothe received I and Q components. For linearity reasons, if the twounknown parameters of an I/Q mismatch, namely, a gain mismatch and aphase mismatch, were a-priory known, then the multiplication of receiveddistorted samples with Cor may yield a signal with significantly reducedor eliminated I/Q mismatch. Since the gain mismatch parameter and/or thephase mismatch parameter may not be a-priory known, Code 1 may implementa LMS algorithm to find substantially best values per iteration. Forexample, Code 1 may determine the value of a gain mismatch (namely,B_est) and the value of a phase mismatch (namely. T_est) that mayminimize the error between the expected signal (namely, Vm) and thedistorted signal (namely. Vr) multiplied by the correction matrix(namely, Cor). This may be performed, for example, by determining valuesthat result in substantially zero gradient of the error function withrespect to the two unknown parameters, namely, the gain mismatchparameter and the phase mismatch parameters. In some embodiments, forexample, the shapes of the gradients (namely, B1 and B2) may beanalytically defined or determined. In one embodiment, for example, thealgorithm may begin with an initial random value, then calculate theerror function, and then iteratively update the estimation of B_est andT_est based on the magnitude and direction of the gradient, therebyminimizing the error function and yielding the best fit for the Cormatrix. Upon finding the best fit, the received samples may bemultiplied by the Cor matrix in order to cancel the I/Q mismatch.

It is noted that Code 1 is presented herein for exemplary purposes only,and embodiments of the invention are not limited in this regard and mayutilize other suitable algorithms, functions, codes, pseudo-codes,instructions, correction matrices, procedures, sets of instructions,schemes, calculations, equations, formulae, parameters, or the like.

FIG. 3 is a schematic flow-chart of a method of I/Q mismatch correctionin accordance with exemplary embodiments of the invention. The methodmay be used, for example, by system 100 of FIG. 1, by device 101 ordevice 102 of FIG. 1, by device 200 of FIG. 2, by processor 210 and/orcorrection unit 212 of FIG. 2, or by other suitable processors,controllers, circuits, units, wireless communication devices, stations,systems and/or networks. In some embodiments, the method may be used,for example, to digitally correct or cancel an I/Q mismatch, or tocorrect or cancel an I/Q mismatch of a signal in a digital format.

As indicated at box 310, the method may include, for example, receivingan I/Q signal, e.g., by processor 201. As indicate at box 320, themethod may include, for example, performing channel estimation based ona Training Sequence (TS) included in the I/Q signal, e.g., by channelestimator 213. As indicated at box 330, the method may includeestimating symbols transmitted in the I/Q signal, for example, usingequalizer 214.

As indicated at box 340, the method may include, for example,re-encoding the estimated symbols, e.g., using re-encoder 215. Asindicated at box 350, the method may include, for example, performingI/Q mismatch analysis, e.g., by correction unit 212. These operationsmay be performed, for example, based on a pre-defined scheme oralgorithm. For example, LMS calculations may be used to estimate an I/Qmismatch, e.g., using an algorithm similar to the algorithm presented inpseudo-code as Code 1.

As indicated at box 360, the method may include correcting or cancelingthe estimated IIQ mismatch. This may be performed, for example, bycorrection unit 212 based on a pre-defined correction matrix orcorrection function, e.g., a correction function similar to thatreflected in Code 1.

As indicated by arrow 370, the channel estimation operations of block320, the symbols estimation operations of box 330, the re-encodingoperations of box 340, the I/Q mismatch analysis operations of box 350,and the I/Q mismatch correcting or canceling operations of box 360, maybe repeated for one or more iterations. In one embodiment, for example,a predetermined number of iterations, e.g., two iterations, of theabove-described operations may be performed. In some embodiments, forexample, the number of iterations may be based on one or morepre-defined criteria, e.g., a series of iterations may be repeated untila calculated I/Q mismatch is smaller than a pre-defined threshold value,or until a pre-defined period of time elapses. In some embodiments,results or corrected data produced in a first iteration may be used asthe starting values for the operations of a second, subsequent,iteration.

In some embodiments, the I/Q analysis operations and/or I/Q correctionoperations of box 350, and the correcting or canceling operations of box360, may utilize a pre-defined algorithm, code, function, correctionmatrix, or scheme. In one embodiment, for example, the method mayinclude using an algorithm similar to the algorithm presented in thepseudo-code of Code 1 above.

Other suitable operations or sets of operations may be used inaccordance with embodiments of the invention.

Some embodiments of the invention may be implemented by software, byhardware, or by any combination of software and/or hardware as may besuitable for specific applications or in accordance with specific designrequirements. Embodiments of the invention may include units and/orsub-units, which may be separate of each other or combined together, inwhole or in part, and may be implemented using specific, multi-purposeor general processors, circuits or controllers, or devices as are knownin the art. Some embodiments of the invention may include buffers,registers, storage units and/or memory units, for temporary or long-termstorage of data or in order to facilitate the operation of a specificembodiment.

Some embodiments of the invention may be implemented, for example, usinga machine-readable medium or article which may store an instruction or aset of instructions that, if executed by a machine, for example, bydevice 101, by device 102, by device 200, by processor 210, bycorrection unit 212, by re-encoder 215, or by other suitable machines,cause the machine to perform a method and/or operations in accordancewith embodiments of the invention. Such machine may include, forexample, any suitable processing platform, computing platform, computingdevice, processing device, computing system, processing system,computer, processor, or the like, and may be implemented using anysuitable combination of hardware and/or software. The machine-readablemedium or article may include, for example, any suitable type of memoryunit (e.g., memory unit 204), memory device, memory article, memorymedium, storage device, storage article, storage medium and/or storageunit, for example, memory, removable or non-removable media, erasable ornon-erasable media, writeable or rewriteable media, digital or analogmedia, hard disk, floppy disk, Compact Disk Read Only Memory (CD-ROM),Compact Disk Recordable (CD-R), Compact Disk Re-Writeable (CD-RW),optical disk, magnetic media, various types of Digital Versatile Disks(DVDs), a tape, a cassette, or the like. The instructions may includeany suitable type of code, for example, source code, compiled code,interpreted code, executable code, static code, dynamic code, or thelike, and may be implemented using any suitable high-level, low-level,object-oriented, visual, compiled and/or interpreted programminglanguage, e.g., C, C++, Java, BASIC, Pascal, Fortran, Cobol, assemblylanguage, machine code, or the like.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents may occur to those skilled in the art. It is, therefore, tobe understood that the appended claims are intended to cover all suchmodifications and changes as fall within the true spirit of theinvention.

What is claimed is:
 1. A method executable by a wireless communicationdevice, the method comprising: receiving an input signal, wherein theinput signal has (i) an in-phase component and (ii) a quadraturecomponent; based on an analysis of a mismatch between (i) the in-phasecomponent of the input signal and (ii) the quadrature component of theinput signal, re-encoding an estimated symbol of the input signal togenerate a re-encoded signal; and multiplying the re-encoded signal by acorrection matrix to correct the mismatch between the in-phase componentand the quadrature component in the re-encoded symbol, wherein thecorrection matrix is based on the in-phase component and the quadraturecomponent.
 2. The method of claim 1, further comprising: analyzing themismatch between (i) the in-phase component of the input signal and (ii)the quadrature component of the input signal.
 3. The method of claim 1,further comprising: estimating the symbol within the input signal. 4.The method of claim 3, further comprising: based on the correctedre-encoded signal, re-estimating the symbol within the input signal. 5.The method of claim 1, wherein the input signal comprises one or moretraining sequences.
 6. The method of claim 1, wherein the correctionmatrix is an inverse matrix of a substantially best value gain mismatchand substantially best value phase mismatch model of the in-phasecomponent and the quadrature component.
 7. The method of claim 6,further comprising: determining, using a Least Mean Square algorithm,(i) the substantially best value gain mismatch and (ii) thesubstantially best value phase mismatch.
 8. The method of claim 1,wherein the input signal is received via a channel, and the methodfurther comprises: estimating the channel; and based upon the correctedre-encoded signal, re-estimating the channel.
 9. A wirelesscommunication device comprising: a receiver configured to receive aninput signal, wherein the input signal has (i) an in-phase component and(ii) a quadrature component; an encoder configured to, based on ananalysis of a mismatch between (i) the in-phase component of the inputsignal and (ii) the quadrature component of the input signal, re-encodean estimated symbol of the input signal to generate a re-encoded signal;and a correction unit configured to multiply the re-encoded signal by acorrection matrix to correct the mismatch between the in-phase componentand the quadrature component in the re-encoded symbol, wherein thecorrection matrix is based on the in-phase component and the quadraturecomponent.
 10. The wireless communication device of claim 9, wherein thecorrection unit is further configured to: analyze the mismatch between(i) the in-phase component of the input signal and (ii) the quadraturecomponent of the input signal.
 11. The wireless communication device ofclaim 9, further comprising: an equalizer configured to estimate thesymbol within the input signal.
 12. The wireless communication device ofclaim 9, wherein the equalizer is further configured to: based on thecorrected re-encoded signal, re-estimate the symbol within the inputsignal.
 13. The wireless communication device of claim 9, wherein theinput signal comprises one or more training sequences.
 14. The wirelesscommunication device of claim 9, wherein the correction matrix is aninverse matrix of a substantially best value gain mismatch andsubstantially best value phase mismatch model of the in-phase componentand the quadrature component.
 15. The wireless communication device ofclaim 9, wherein (i) the substantially best value gain mismatch and (ii)the substantially best value phase mismatch is determined using a LeastMean Square algorithm.
 16. The wireless communication device of claim 9,wherein the input signal is received via a channel, and wherein thewireless communication device further comprises: a channel estimatorconfigured to estimate the channel, and based upon the correctedre-encoded signal, re-estimate the channel.